1. Field of the Invention
The present invention relates to corrosion protection of an appliance constituted by metallic pipes and a pipeline device as a part thereof, more particularly, a technology for preventing corrosion caused by condensation at exposed metal pipe parts of a heat exchanger or the like.
2. Discussion of Background
In a pipeline device constituting a main part of a cooling apparatus, metal pipes in which a refrigerant at a temperature different from that of the external air flows are used. For example, in the production of a heat exchanger used for a refrigerator, an air conditioner or the like, a pipeline structure of continuous metal pipes is prepared by skewering metal pipes into fins of aluminium thin sheets laminated or arranged at optional intervals as flow paths of a fluid such as air, fixing the metal pipes, and connecting bends of U-shaped metal pipes to both ends of the metal pipes. By permitting a refrigerant to flow in a plurality of metal pipes disposed in such a continuous pipeline structure passing through both ends of the laminated fins, the heat of the refrigerant can be transmitted through the metal pipes to obtain a desired temperature. Accordingly, by permitting the external air to flow between the fins to conduct temperature change, this device shows a heat-exchanging function for cooling or heating.
In a case of metal pipes through which a medium of a temperature higher than room temperature flows, the surface of the metal pipes is chemically stable, since the dried state is maintained and only a gaseous state fluid flows. However, in a case where a medium of a temperature lower than room temperature flows through the metal pipes, if the temperature of the flowing gas (for example, air as atmosphere) is lower than the dew point, condensation at the metal pipe surface makes the surface active, and when the atmosphere contains an acid or a base capable of corroding the metal, the condensed water accelerates the corrosion (pitting corrosion) at the exposed portion, by which leakage of the medium flowing through the metal pipes may sometimes be caused.
As a method for preventing such a problem, a method has been employed wherein a metallic foil having a sacrificial corrosion effect is used for covering. For example, in an aluminium evaporator of a cooler unit for air conditioning introduced in JP-UM-A-60-170684, for the purpose of preventing the outer surface corrosion of a flattened aluminium tube of the evaporator, a method is proposed wherein a sacrificial corrosive material formed by a metallic foil of e.g. zinc or tin, is pressed to the exposed portion of the metal pipe by use of a metallic foil-attaching member, and fixed thereto.
By this method, even if water penetrates into the portion to which the metallic foil is attached, galvanic corrosion is caused at this portion and the metallic foil having an electric potential lower than that of the flattened aluminium tube is selectively corroded, whereby the corrosion of the flattened aluminium tube can be prevented.
Hereinbelow, the above prior art will be described in detail with reference to the drawings. FIGS. 4 to 9 are explanatory drawings showing the corrosion protection method of the exposed portion of the metal pipe disposed in conventional heat exchangers. FIG. 4 is a cross-sectional view illustrating an example of corrosion protection of a side face of a flattened aluminium tube of a cooler unit for air conditioning. FIG. 5 is an enlarged view of a main part of FIG. 4. FIG. 6 is a perspective view of a metallic foil 11 as shown in FIG. 5.
In FIG. 4, for the purpose of preventing the corrosion of the outer surface of the flattened aluminium tube, a sacrificial corrosion material is formed by press molding a metallic foil of e.g. zinc or tin against the outer surface portion of the flattened aluminium tube by use of a metallic foil-attaching member. FIG. 4 is a cross-sectional view illustrating an example of corrosion protection at the side portion of the flattened aluminium tube. FIG. 5 is an enlarged view of a main part of FIG. 4. Here, as the material for the tube 4, an aluminium alloy of JIS (Japanese Industrial Standard) A1050, A3003 or the like, is used, and as the material for a fin 5, an aluminium alloy having an electric potential lower than that of the material for the tube 4, for example, JIS A7072 is used, by which the fin is constructed so that it undergoes sacrificial corrosion.
In the figures, 1 is an evaporator, 2 is a case, 3 is a heat insulating material, 4 is a flattened tube, 4a and 4b are bent portions, 5 is a corrugate fin, 8 and 9 are pipes, 11 is a metallic foil as a part of a corrosion proof member, C is an outer surface which is in contact with the heat insulating material 3, and D is a smooth metal surface. The process of operation for preparing the above structure will be described below. Firstly, 11 is a metallic foil interposed between the heat insulating material 3 and the outer surface of the lower bent portion 4b of the flattened tube 4, an outlet pipe of an expansion valve or the pipe 8 or 9. In this example, as the metallic foil, a foil integrally formed by pressing as shown in FIG. 7(a) or FIG. 7(b) is used. The metallic foil 11 may be made of the same material as the fin 5. Otherwise, any material may be used so long as it shows a corrosion effect by the sacrificial corrosion of the tube 4 of e.g. zinc. The thickness of the metallic foil 11 is preferably from 40 to 200 xcexcm. The metallic foil 11 is formed into a shape fitting on the lower bent portion 4b of the flattened tube 4 and the pipes 8 and 9, and interposed between the evaporator 1 and the heat insulating material 3 for assembling.
According to the above measures and structure, since the metallic foil 11 as the corrosion proof member is pressed and bonded to the outer surface C of the lower bent portion 4b of the flattened tube 4, the corrosion protection effect by the sacrificial corrosion of the metallic foil 11 acts directly on the outer surface C, whereby the corrosion of the outer surface C can effectively be prevented. Further, the same corrosion protection effect can be given for other portions such as pipes 8 and 9.
As examples of similar techniques, certain measures have been introduced wherein a metal having a sacrificial corrosion function is applied to the back surface of the metallic foil 11 and this foil is fixed on the case 2. Such measures may include fixing of the metallic foil on the heat insulating material 3 by use of an adhesive as illustrated in FIG. 8, or uniform coating of metal powder on the heat insulating material 3 by use of a resin having an adhesion function as illustrated in FIG. 9. In both cases, the metallic foil 11 for the sacrificial corrosion is bonded to the case 2 in such a state that the foil 11 is pressed to the outer surface C of the lower bent portion 4b of the flattened tube 4, by which the outer surface C is protected from corrosion by the corrosion proof effect obtainable by the sacrificial corrosion of the metallic foil 11.
However, for the method of bonding the metallic foil of e.g. zinc or tin in the above measures, it is important to fit the metallic foil well on the case 2 as the corrosion proof member at the time of production. If the metallic foil is provided in an overly stretched state to the case having concaves for closely bonding it to pipes for which corrosion protection is to be given, there are drawbacks that the metallic foil tends to be torn when the corrosion proof member having them integrated is closely bonded to the pipes or used under the condition that stress is applied by vibration or temperature change.
Further, if the metallic foil is provided with looseness, folds and consequently wrinkles will be formed. Accordingly, as in the above case where the metallic foil is torn, the metallic foil having the sacrificial corrosion protection is not bonded in some parts of the flattened tube surface. As a result, not only the corrosion proof effect by the sacrificial corrosion can not be obtained, but also stagnation of condensed water tends to occur, whereby corrosion (pitting corrosion) will be formed at that portion on the flattened tube surface, leading to worse result which spoils the reliability on use, for example, leakage of a refrigerant by the formation of corrosion holes.
Further, substantial skill is required to conduct operations without forming the parts to which no metallic foil is bonded on the flattened tube surface, in order to remove the above problems in the operation. Accordingly, there is a drawback that it is difficult to accomplish simplification of operations including automating or the like in the production of the evaporator.
Under such circumstances, the present invention has been accomplished. It is an object of the present invention to provide a pipeline device having a means for easily and efficiently accomplishing corrosion protection, having a high reliability and a method for its production, by which metal pipes of e.g. copper in a pipeline device such as a heat exchanger used under a high humidity atmosphere, are protected from pitting corrosion and ants"" nest-like corrosion due to condensation or attachment of a corrosive gas.
The first aspect of the present invention relates to a pipeline device which comprises a metal pipe to be disposed on or connected to an appliance in a state such that an outer periphery of the metal pipe is exposed to air or in contact with moisture or a corrosive gas, in which a refrigerant of a temperature lower than the temperature of the outside flows, and a corrosionproof coating containing a powdery material of a metal or a metal salt, is coated on the outer periphery of the metal pipe.
The second aspect of the present invention is that the powdery material of a metal or a metal salt has a polarization potential lower than the polarization potential of the metal pipe.
The third aspect of the present invention is that the corrosionproof coating is at least one selected from the group consisting of a mixture of a water-soluble coating and zinc phosphate, a mixture of a water-insoluble coating and zinc, and a mixture of a thermoplastic resin and zinc.
The fourth aspect of the present invention is that the pipeline device further comprises fins for transmitting the heat in the metal pipe to an outside of the metal pipe, the fins being provided in contact with the outer periphery of the metal pipe via the corrosionproof coating.
The fifth aspect of the present invention relates to a method for producing a pipeline device, which comprises a step of forming into a desired shape a metal pipe to be disposed in a state that an outer periphery of the metal pipe is exposed to air or in easily contact with moisture or a corrosive gas; and one of the following steps (a) and (b):
Step (a): coating a corrosionproof coating containing a powdery material of a metal or a metal salt on the outer periphery of the metal pipe; and bringing fins for transmitting the heat in the metal pipe to an outside of the metal pipe into fixedly contact with the outer periphery of the metal pipe;
Step (b): fitting fins for transmitting the heat in the metal pipe to an outside portion of the metal pipe, to the outer periphery of the metal pipe; and coating a corrosionproof coating containing a powdery material of a metal or a metal salt on the outer periphery of the metal pipe,
wherein the powdery material of a metal or a metal salt has a polarization potential lower than the polarization potential of the metal pipe.
The sixth aspect of the present invention relates to the method wherein the corrosionproof coating is a mixture of a water-soluble coating and zinc phosphate, or a mixture of a water-insoluble coating and zinc.
The seventh aspect of the present invention relates to the method wherein the corrosionproof coating is coated on the outer periphery of the metal pipe by immersing the metal pipe in a thermoplastic organic resin fluid in a heated and molten state or in a powdery state.
The eighth aspect of the present invention relates to a heat exchanger which comprises a metal pipe for exchanging heat with a fluid flowing in the metal pipe, and fins which are in fixedly contact with an outer periphery of the metal pipe, for exchanging the heat between the metal pipe and air outside the metal pipe, wherein at least a part of the outer periphery of the metal pipe is coated with a corrosionproof coating containing a powdery material of a metal or a metal salt, and the powdery material of a metal or a metal salt has a polarization potential lower than the polarization potential of a material constituting the metal pipe.
The ninth aspect of the present invention relates to the heat exchanger wherein the corrosionproof coating is at least one selected from the group consisting of a mixture of a water-soluble coating and zinc phosphate, a mixture of a water-insoluble coating and zinc, and a mixture of a thermoplastic resin and zinc.
The tenth aspect of the present invention relates to the heat exchanger wherein the fins are fitted to the outer periphery of the metal pipe with the corrosionproof coating interposed.